As a related art of the present invention, FIG. 1 illustrates coverage and capacity optimization (CCO) in a self-organizing network specified in third generation partnership project (3GPP) technical report (TR). As a use case of CCO, the 3GPP TR proposes a technology in which a small cell base station periodically observes two-dimensional (2D) distribution of UE in the cell and adjust coverage, and defines use of the timing advance Taw and the angle of arrival (AOA) of UE for the purpose. However, according to this technology, when pieces of UE are in motion, calculation of the AOA is complicated, and also coverage holes may be generated, which may cause a discontinuous service.
As another related art of the present invention, FIG. 2 illustrates a power setting method and femtocell base station and UE technology for the power setting method disclosed in Korean Unexamined Patent Application Publication No. 10-2011-0042508. This technology is characterized by a method of setting power in a femtocell base station including an operation of setting initial power to set femtocell coverage, an operation of receiving a handover request message from macrocell UE, an operation of acquiring the position of at least one piece of femtocell UE which is communicating within the femtocell coverage, and an operation of setting transmission power to increase or decrease every 1 m based on the position of the at least one piece of femtocell UE communicating within the femtocell coverage. However, this technology is configured to adjust transmission power based on only the position of femtocell UE, and thus the capacity of a femtocell base station cannot be optimally used. Also, in a place in which pieces of UE are concentrated (e.g., a sports field), overload may occur in a femtocell base station, or the femtocell base station may malfunction to repeatedly increase and decrease transmission power.
As still another related art of the present invention, FIG. 3 illustrates an apparatus and method for output power control of a home base station disclosed in Korean Unexamined Patent Application Publication No. 10-2009-0062192. This technology includes a process of determining the type of a user who has transmitted a position registration message when the position registration message is received, a process of calculating a maintenance power when the type of the user is a home user, and a process of increasing an optimal output power value to be applied to a home base station by a difference between the maintenance power and the most recently calculated power for avoiding interference when the maintenance power is not greater than the interference avoidance power. However, according to this technology, it is necessary to perform an additional operation of UE, and it is not possible to optimally use the capacity of a home base station because a maintenance power value is calculated based on the most recently calculated interference avoidance power.
This work was supported by the ICT R&D program of MSIP/IITP, Republic of Korea. [13-911-05-001, Development of OpenFlow-based integrated management system for wired and wireless network]